Biology of Reproduction, Vol 21, 683-689, Copyright © 1979 by Society for the Study of Reproduction

Factors Affecting Estrogen-Induced LH Release in the Cow

¹ Livestock and Range Research Station, U.S. Department of Agriculture and Montana Agricultural Experiment Station, Miles City, Montana 59301

Six experiments were conducted to study the mechanisms controlling estrogen-induced luteinizing hormone (LH) release in the cow. Estradiol-l7 (E₂) induced a release of LH in ovariiectomized cows at doses ranging from 0.25-10.00 mg and estrone (E₁) was less effective than E₂. Exogenous progesterone (P₄), administered s.c. in a silicone rubber implant for periods of 2-9 days prior to E₂ injections, did not inhibit the E₂-induced LH release even when a very low dose (0.25 mg) of E₂ was given. However, when a corpus luteum (CL) was present and endogenous P₄ was more than 1 ng/ml, E₂ did not induce an LH release. Possible mechanisms for this discrepancy between the effects of exogenous and endogenous P₄ are discussed. Suckling and/or lactation inhibited the E₂-induced LH release for at least 2 weeks postpartum. This inhibition may partially explain postpartum anestrus.

Note:
ACKNOWLEDGMENTS The authors express appreciation to Dr. G. D. Niswender, Colorado State University, Fort Collins, for anti-bovine LH serum, Dr. L. E. Reichert, Jr., Emory University, Atlanta, GA, for purified bovine LH and NIAMDD for NIH-LH-B8.

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